Transistors, in particular power transistors such as power MOSFETs or power IGBTs, can be used as switches for switching electrical loads. Such loads may be inductive loads such as electric motors or solenoid valves. When the transistor is driven in the ON state, inductive loads absorb electrical energy, which must be commutated via a turn-off commutation circuit when the transistor is driven in the OFF state.
The transistor itself can be part of a turn-off commutation circuit that is used to convert the electrical energy stored in the load into heat. A semiconductor substrate or semiconductor chip in which the transistor is integrated heats up during load turn-off commutation. In this case, a critical operating state should be prevented in which there is a risk of damaging or destroying the transistor.
The thermal power that a transistor can absorb without reaching a critical operating state depends on various parameters such as the chip area or the existence of special cooling measures such as heat sinks. Power-transistor datasheets contain maximum values, which should not be exceeded, for power dissipation, turn-off commutation energy, permitted current, inductance to be switched or duty cycle. Whether the customer actually heeds this specification, however, is outside the control of the power transistor manufacturer.